Chemical machining of nickel in ferric chloride solution

Abstract

Chemical machining is a method of removing an unmasked area from a metal surface by controlled selective dissolution with chemical reagents. This process is used in the production of machine and electronic parts and is also called chemical etching or system. milling. Sometimes current is applied at low current density as an assist. Many detailed studies have been 101 conducted recently to investigate the chemical etching of nickel and nickel alloys [1-3]. Nickel is highly resistant to a variety of corrosive media, due to the passive film that it forms on its surface. Moon and v Nobe [4] reported that the dissolution rates of nickel 1 0 0 increase as the concentration of chloride ions is E increased. Chevalet and Zutic [5] also proposed a reaction mechanism of nickel in chloride solution. The purpose of this study was to investigate the ~ol etching behaviour of nickel in ferric chloride solu._c tions over the temperature range 15-50°C. The ~ 10 -1 experiments were conducted by a gravimetric "' method. Low current densities were applied to enhance the etching rate of nickel in FeC13 solution in this study. Nickel specimens were prepared for etching tests from 99.99% purity nickel sheet (0.5 m m x 2.5 cm x2 .hc m) . The specimens were polished with 1000-grade silicon carbide paper, cleaned in acetone and dried. The prepared specimens were then used in immersion tests. For the measurement of etching rates, 1000ml t01 solutions were prepared in a constant-temperature water bath at a temperature (+ 0.5 °C) over the range 15-50 °C. Weighed specimens were totally 4" immersed for a period of 1 h at the end of which they were removed, rinsed in 10% sulphuric acid followed by distilled water and acetone, and then dried E and reweighed. For the purpose of accelerated etching for nickel specimens, a Nichia model G1001ED galvanostat o, was used to apply a constant anodic current on the .E enickel. Current densities of 0.01-0.1 Acm -2 were chosen to compare with the results from immersion tests. For the etching of nickel good and reproducible results were obtained. Results for the test solutions in the concentration range from 0.1 to 1.0 M at 26 °C are shown in Fig. 1. It is clear that the etching rate of nickel increases exponentially with FeC13 concentration. The etching rate of nickel in FeC13 containing